Cancer is the most common comorbidity in septic patients with nearly 93,000 cases annually. Importantly, cancer is also the comorbidity associated with the highest risk of death in patients with sepsis. We have created a murine model that replicates the increased mortality seen in septic patients with cancer compared to previously healthy patients who develop sepsis. The first goal of this proposal is to understand possible mechanisms through which pre-existing cancer increases mortality when a host develops sepsis. Based upon preliminary data, both the immune system and gut integrity appear to be involved, so each of these will be examined in detail. Experiments will be performed in multiple models of sepsis with multiple tumor lines to determine whether results are generalizable or specific to either type of sepsis or type of cancer. Additionally, there is extensive data from multiple investigative groups that apoptosis prevention in either lymphocytes or the gut epithelium improves survival in previously health rodents with sepsis. However, when this strategy is used in septic mice with cancer, the precise opposite is found with apoptosis prevention either markedly increasing mortality (lymphocytes) or losing its efficacy (intestine). The proposal seeks to understand why a beneficial therapy that has widespread acceptance as a possible treatment approach for patients turns deadly if sepsis occurs in the setting of cancer. Since efforts are currently being made to translate apoptosis prevention into treatment that can be used at the bedside for septic patients, this proposal could potentially change entry criteria and/or prevent inadvertent mortality in patients undergoing clinical trials of apoptosis prevention in sepsis. Thus, the proposal seeks to understand a subpopulation within sepsis that may require a different therapeutic approach than a typical septic host, and this may have significant implications in a disease that is both very common and highly lethal.